Undoubtedly the greatest claim for this vaporizer is the fact that practically no carbon deposit forms upon the inside of the cylinder or on the piston. What little deposit is formed takes the shape of small, soft flakes, which, instead of adhering to the cylinder walls, break away before they have attained any size and are blown through the exhaust valve. Altogether, this device seems to have finally solved the problem of using kerosene as a fuel on air-cooled engines, especially if the carbon deposit difficulty has been finally overcome. The device was fitted to a 3½ h.p. Matchless with a White and Poppe engine. In order to start up, a small gasoline tank, holding about one half-pint of gasoline, is fitted under the main tank and communicates with the feeder. Half a minute is all that is necessary running on gasoline, when the kerosene can be turned on. The machine would fire at a walking pace, and could also be accelerated up to 55 m.p.h. CHAPTER X LUBRICATION (116) General Notes on Lubrication. No matter how carefully the surface of a shaft or bearing may be finished, there always remains a slight roughness or burr of metal, which although of microscopic proportions is productive of friction or wear. Each minute projection of metal on a dry shaft acts exactly as a lathe tool, when the shaft revolves in cutting a groove in the stationary bearing. Since there are a multitude of these projections in a journal, the wear would be very rapid, and would in a short time completely destroy either the shaft or bearing, no matter how highly finished in the beginning. When lubricating oil is introduced into a bearing it immediately covers the rubbing surface, and as the oil has a considerable resistance to being deformed, or is “stiff,” it separates the surface of the shaft from that of the bearing for a distance equal to the thickness of the oil film. With ordinary lubricants this distance is more than enough to raise the irregularities of the shaft out of engagement with those of the bearing. This property of “stiffness” in the oil is known as “viscosity.” The value of viscosity varies greatly with different grades of oil, and also with the temperature with the result that the allowable pressure on the oil per square inch also varies. With oils of low viscosity a small pressure per square inch on the bearing will squeeze it out, and allow the two metallic surfaces to come against into contact, causing wear and friction, while an oil of greater viscosity will successfully resist the pressure. The life and satisfactory operation of the engine depends almost entirely upon the lubricant and the devices that apply it to the bearings. Excessive wear and change in the adjustments are nearly always the result of defective lubricating devices or a poor lubricant. The principal lubricants are: (1) Solid lubricants such as graphite, soapstone, or mica.